In the completion of oil wells the practice is to drill a well bore from the earth's surface, insert a tubular steel casing in the well bore and fill the annulus between the casing and well bore with a cement slurry which hardens to support the casing in the well bore. Thereafter, a deeper section of well bore with a smaller diameter than the surface casing is drilled. The drilling bit is removed and a liner, which is a string of connected lengths of tubular, steel pipe joints, is lowered through the casing and into the open well bore. The liner at its upper end is attached to a setting tool and liner hanger which, in turn, are attached to a string of drill pipe which supports the weight of the liner on the setting tool as the tool and liner assembly are being lowered into the open borehole. The length of the liner is predetermined usually so as to have its lower end proximate to the bottom of the open well bore with an upper end section and an attached liner hanger overlapping the lower end of the section of casing above. The setting tool is operated to set slips on the liner hanger against and in gripping engagement with the casing so that the liner is "hung" or suspended in the open well bore by the slips in the lower end of a casing or pipe. With a hydraulically operated setting tool, the slips are set by dropping a check valve ball or plug into a removable valve seat in the section of open pipe attached to the setting tool in a location below the hydraulic actuating system. Next, by building up pressure in the drill pipe the slips are set by the hydraulically operated mechanism in the setting tool. Thereafter, by increasing the pressure in the drill pipe, the removable valve seat is sheared out of the bore of the open pipe below the setting tool and falls into the liner. The setting tool then is released from the liner hanger. When the setting tool is released from the liner hanger, the exterior of the open pipe below the setting tool remains sealed off with respect to the bore of the liner so that a cement slurry can be pumped down the drill pipe through the open pipe and through the liner. At the lower end of the liner is a cementing shoe and back pressure valves (sometimes called cementing float equipment) and the slurry of cement is displaced by surface pumping equipment to flow through the cementing shoe and into the annulus between the liner and the open well bore. The cement slurry is displaced upwardly until the volume of cement in the annulus is at a desired level which is generally a level overlapping the top of the liner above. During this operation there is mud or control fluid in the well bore and mud or control fluid driving the cement slurry. Thus, when the cement slurry is introduced through the drill pipe it is generally followed by a cementing plug which wipes the internal surface of the drill pipe as it is moved through the drill pipe to minimize contaminating the cement slurry with mud or control fluid. When the cementing plug reaches the setting tool it latches into a liner cement wiper plug (which is usually typically larger in diameter than the I. D. of the drill pipe) and the liner cement wiper plug then follows the cement slurry. The liner cement wiper plug wipes the I. D. of the liner. The liner cement wiper plug stops when it bumps a landing collar or float equipment in the liner.
As noted above, in the setting operation for the liner hanger with a hydraulic setting tool, it is customary to drop a ball which seats in a ball valve seat in the setting tool at a valve seat location below a hydraulic actuating means. Thus, when hydraulic pressure is applied to the drill pipe the hydraulic pressure actuates the setting mechanism for setting the slips on the liner hanger. Once the slips are set and the liner is hung, the hydraulic pressure in the drill pipe can be increased to shear a shear pin in the ball valve member to release the ball valve member and ball and permit them to be removed from the end of the drill pipe, or alternatively, to open a valve in the drill pipe.
In certain completion operations the above described system is not as economical and efficient as might be desired. For example, where the ID of the liner casing is extremely large, it is not only necessary to wipe the entire cross-section of the liner with a liner plug but also the displacement volume is significantly large which causes problems in longer cement placement time. Also, liners can have two or more sections with different diameters so that cementing plugs may wipe in one size diameter but not another.
As a result of the above noted problems and various other reasons, heretofore from time to time, the practice has been to lower a liner hanger to the desired location and hang the liner as above described. After the liner is hung, the setting tool and attached drill pipe are removed from the well bore prior to the cementing operation. Next, drill pipe with a polished mandrel at its lower end is lowered into the liner until the polished mandrel enters and seals with respect to a sealing bore located at the lower end of the liner. Typically, the sealing bore is part of the float collar or the float shoe. With this arrangement then, cement slurry can be pumped directly through a drill pipe and through the cementing equipment at the lower end of the liner neither contacting the internal bore of the liner nor imposing any pressure to the bore of the liner. However, as can be appreciated, this system requires two trips of a drill pipe, i.e., a first trip of drill pipe with a setting tool to hang the liner and a second trip of drill pipe with a polished surface mandrel to utilize the drill pipe in a sealed bore at the lower end of the liner.